Microtitration plate

ABSTRACT

A microtitration plate, having a frame made of a plastic which has a plate with a multiplicity of holes, and a multiplicity of receptacles made of the same plastic which are fixedly connected to the plate at the holes by directly molding them thereto, have a receiving portion protruding from the underside of the plate, and are accessible from the upper surface of the plate through apertures.

RELATED APPLICATIONS

This application is a continuation of pending U.S. application Ser. No.10/393,911 filed Mar. 21, 2003, which is incorporated by referenceherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a microtitration plate.

2. Description of the Prior Art

Microtitration plates are used for most varied microbiological, cell-breeding, and immunological techniques. In particular, microtitrationplates are employed for the PCR or the breeding of microorganisms orcells.

Microtitration plates have already been known which have a frame with aplate to which a multiplicity of receptacles are fixed which have areceiving portion protruding from the underside of the plate and areaccessible from the upper surface of the plate through apertures. Thereceptacles are also referred to as “wells”. The current 96-receptaclemicrotitration plates have 8×12=96 receptacles in rows and columns.However, microtitration plates having a larger number of receptacles areused more and more.

Single-component microtitration plates in polystyrene are unsuitable forthe PCR, particularly because the softening temperature of this plastic(about 85° C.) is exceeded during the PCR.

Conventional single-component microtitration plates in polypropylene aregenerally adapted to be used for the PCR. However, they are flexurallysoft, tend to be distorted, are uneven and can be manufactured only atlarge tolerances and undergo large tolerance variations when in use.Specifically, they are not particularly suited for being handled byautomatic devices because their softness makes it difficult forautomatic devices to grip them. Further, their low dimensional stabilitymay have the consequence that the proportioning needles will contact thewalls while being introduced into the receptacles. Furthermore, heattransfer into the walls is poor because the thick walls of thereceptacles resist to it, which is adverse to temperature regulation andthe length of cycle times during the PCR.

EP 1 161 994 A2 discloses a microtitration plate with a frame made of astiff first plastic which has a plate with a multiplicity of holes, anda multiplicity of receptacles made of a second plastic suited for thePCR and/or exhibiting permeability to oxygen, which are fixedlyconnected to the plate by directly molding them thereto, have areceiving portion protruding from the underside of the plate and areaccessible from the upper surface of the plate through apertures. Thefirst plastic may be chosen so as to impart to the frame the desiredstiffness for being handled by an automatic device. This documentfurther discloses a manufacturing process in which the frames andreceptacles of the microtitration plate are produced in a multicomponentmolding procedure.

Therefore, it is the object of the invention to provide anothermicrotitration plate having more favorable characteristics in use.

In addition, a technique for the manufacture of the microtitration plateis intended to be provided.

SUMMARY OF THE INVENTION

The object of the invention is achieved by a microtitration plate havinga frame made of a plastic which has a plate with a multiplicity ofholes, and

-   -   a multiplicity of receptacles made of the same second plastic        which are fixedly connected to the plate by directly injection        molding them to each other at the holes, have a receiving        portion protruding from the underside of the plate, and are        accessible from the upper surface of the plate through        apertures.

Hence, the inventive microtitration plate is made of a single plasticonly. Unlike conventional single-component microtitration plates whichare completely molding in a single injection molding process, theinventive microtitration plate has the frame and receptacles molded toeach other in two injection processes. This makes it possible to meetthe requirements made to the frame and receptacles by giving the frameand receptacles a particular configuration and employing moldingprocesses specifically adapted thereto while using a single plasticonly. Injection molding to each other allows to achieve short flow pathsof the plastic material in the frame and in the receptacles, which helpsto achieve an increased injection pressure and to mold the contours ofthe frame and receptacle more easily. Thus, the receptacles can bemolded to have particularly thin walls, specifically for high heatconductivity in view of their use in the PCR. Further, the relativelythick-walled design of the frame which can even be stiffened by ribs andother structures may make the microtitration plate suitable for beinghandled by an automatic device. In addition, the microtitration platehas the advantage that the receptacles may be injection molded onlyafter the plate is molded and undergoes shrinkage, which allows toachieve microtitration plates which are particularly stabledimensionally. Moreover, the plastics of the frame and receptacles canbe fused to each other at the injection molding points (points ofinjection) in the area of the holes so that the frame and receptaclesare connected in a material fit and, thus, are connected to each otherparticularly firmly. This can also be accomplished by melting on theplastic which has been molded first and has solidified already, by meansof the heat of the plastic which is molded later, which causes it to befused to the second plastic.

Generally, the connection of the receptacles to the frame can be made bya material fit and/or a formlocking and/or forcelocking fit. Itpreferably is made in a forcelocking fit by molding the receptacles toholes having varying cross-sections in an axial direction and/or to theexternal area of the holes on at least one side of the plate whileconnecting them thereto in a formlocking fit. A formlocking fit, forinstance, may be achieved by utilizing a different shrinkage behavior ofthe frame and receptacles.

As mentioned previously, molded the receptacles to each other in adirect way makes possible very short flow paths of the material inmolding, which allows to achieve particularly small wall thicknesses ofthe receptacles. These are preferably in the range of about 0.05 to 0.25mm and, in particular, may be about 0.1 mm. This favors heat transfer.For this purpose, the receptacle bottom of each receptacle has providedthereon a molding point from which the material fills a first wallportion of a reduced wall thickness and an upper wall portion connectedto the plate. It is preferred that the upper wall portion be designed asa collar of an increased wall thickness, which allows to manufacture themicrotitration plate at particularly low tolerances.

Hence, since the frame and the receptacles are molded in two steps thebest solutions possible will be achieved with materials which do notnecessarily correspond optimally to the desired functions of the frameand receptacles. Higher rigidity, better planarity, a lower tendency todistortion, and smaller tolerances are ensured by the configuration ofthe frame and a molding procedure adapted thereto. It is preferred thatthe frame of the microtitration plate be provided with a borderingprotruding from the underside which enhances stability, may form asurface to stand on, and offers a surface to be clasped by the automaticdevice. It is advantageous for the frame to have several edge-sidedmolding points (about four to six). The extremely thin walls for betterheat transfer are achieved by moulding the receptacles separately. Noframe is filled via the receptacles so that the full pressure gradientis available only for one receptacle each.

The plastic, in particular, may be a material which is suited for thePCR because of its increased resistance to temperature and reducedaffinity or neutrality to the DNA or other substances. A microtitrationplate made of polypropylene is particularly beneficial for the PCR. Itis preferred that it is pure polypropylene which, in particular, is freefrom protein-containing additives or fillers. However, to increase itsstrength, the polypropylene may generally contain other fillers which donot contain protein. Thus, for instance, it appears possible to employhigh-purity fiber glass as a filler.

According to another aspect, the plastic is a polycarbonate. Thepolycarbonate used for the PCR is preferably a particularlytemperature-resistant and/or chemical-resistant polycarbonate.

Finally, according to an aspect, the plastics of the frame andreceptacles are of different colors. A differentiation is possible here,in particular, by coloring the plastics black and white for the frameand receptacles, respectively. For instance, this makes it easier tooptically check the position of the microtitration plates andreceptacles.

According to the inventive manufacturing technique, the frame andreceptacles are produced in a multi-component molding technique. In thesimplest case, it is a two-component injection molding technique or“twin-shot” technique.

Generally, the sequence of molding the frame and receptacles is random.For manufacture at particularly low tolerances, it is preferred to moldthe frame initially and the receptacles subsequently. This has theadvantage that the frame first may undergo a certain shrinkage orreduction in volume before the receptacles are molded thereto. This isbeneficial, in particular, for crystalline or partially crystallineplastics such as polypropylene which undergo heavy shrinkage followingthe injection molding process. The time interval from molding the frameto molding the receptacles thereto may be chosen so that the shrinkageof the frame (by cooling it down) essentially is effected completely.Once the receptacles are molded on shrinking techniques virtually do notimpair the dimensional stability of the microtitration plate any longer.It specifically is the local tolerance of the receptacles which, thus,can be confined to very low values (about±0.15 mm around theirtheoretical positions). This makes it easier to introduce proportioningneedles with no wall contact.

It is particularly advantageous here if the upper wall region of thereceptacles is designed as a collar of an increased wall thicknessbecause the collar may compensate for hole position tolerances that haveremained during molding.

According to an aspect, the frame having undergone molding is initiallymalleablized, after which the receptacles are molded to the frame.Malleablizing the frame can cause the crystalline structure of the frameto disappear completely. This can be accomplished, for instance, bymalleablizing it at a temperature of up to about 120° C. over a periodof about one hour, as a maximum. It is particularly a frame inpolypropylene which can completely shrink under the conditionsmentioned.

According to an aspect, the plastics of the frame and receptacles are ofdifferent colors.

This microtitration plate is preferably manufactured again by amulti-shot molding technique, particularly a two-shot technique(“twin-shot” technique).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in more detail with reference to theaccompanying drawings of different embodiments. In the drawings:

FIG. 1 shows a 96 type microtitration plate with a frame and receptaclesmade of various plastics in a plan view;

FIG. 2 shows the same microtitration plate in an oblique perspectiveview from bottom; and

FIG. 3 shows the same microtitration plate in a largely magnifiedvertical section-in-part through the plate of the frame and areceptacle;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 through 3, a microtitration plate 1 comprises aframe 2 and a multiplicity of receptacles 3. There is a total of 96receptacles 3 in 8 columns and 12 rows.

The frame 2 has a substantially rectangular plate 4 the outer edge ofwhich is surrounded by a bordering 5 which protrudes approximatelyperpendicularly from the underside of the rectangular plate 4, i.e.beyond the receptacles 3. At bottom, the bordering 5 as is known has anexpansion 6, which enables stacking on the upper surface of anappropriate microtitration plate 1.

The frame 2 has a total of 96 holes 6 in the rectangular plate 4. Thesehave a course of cross-section which widens towards the upper surface 7of the rectangular plate 4 in two portions of different conicity andtowards the underside 8 of the rectangular plate 4 in a conical portion.

In a first molding step, the frame 2 is integrally molded from aplastic. It is preferred to use a high-purity polypropylene, possiblywith a protein-free filter which, when cured, imparts a certainstiffness to the frame 2. The molded points are at the edge of frame 2,e.g. at the lower edge of the bordering 5.

At their base, receptacles 3 have a cup-shaped bottom 9 which isbordered by a conical wall portion 10 of a very small wall thickness(abt. 0.1 mm) Above it, there is a wall portion 11 the wall thickness ofwhich gradually increases towards the top. At its outside, it has thesame conicity as has the wall portion 10. At its inside, however, it isdesigned nearly cylindrically, which results in an approximatelywedge-shaped course of cross-section.

Wall portion 11 terminates in a collar 12 which also is of a largelyincreased wall thickness with respect to wall portion 10. Receptacles 3are molded to rectangular plate 4 in the area of collar 12. To this end,collar 12 externally bears against the inner periphery of holes 6′. Itfurther has a projection 13, 14 each at the upper surface 7 and theunderside 8 of rectangular plate 4, which makes a safe connection torectangular plate 4.

In the area of collar 12, receptacles 3 have a cross-section expandingtowards the top in two portions of different conicity. The receptaclesare accessible from the upper surface of plate rectangular 4 throughapertures 15.

All of the receptacles are simultaneously molded directly to the frame 2and the holes 6′ thereof. Each receptacle 3 has a central molding pointof its own at the underside of bottom 9. This helps achieve shortermolding paths which are made possible by the particularly small wallthickness in wall portion 10. There is a specific suitability of thereceptacles for use in the PCR if polypropylene is used is as a plasticmaterial. The required stiffness of the frame 2 for being handled by anautomatic device can be ensured by giving it appropriate dimensions andbracing it accordingly or incorporating appropriate fillers.

1-22. (canceled)
 23. A microtitration plate for use for automatedpolymerase chain reaction (PCR), comprising: a frame (2) which has aplate (4) wherein the plate (4) has a multiplicity of holes (6′) moldedof a polypropylene; and a multiplicity of thin-wall receptacles (3)having a wall thickness of from about 0.05 to about 0.25 mm at least inone wall portion, and made of the same type of polypropylene as theframe (2) and the plate (4), with the receptacles (3) fixedly connectedto the plate (4) at the holes (6′) by fusing to each other the identicaltype of polypropylene of the receptacles (3) and the plate (4) due todirect molding of the receptacles (3) to the plate (4), the receptacles(3) having receiving portions (9, 10, 11) protruding from the underside(8) of the plate (4), and are accessible from the upper surface (7) ofthe plate (4) through apertures (15), wherein the frame (2) and thereceptacles (3) are composed of the identical type of polypropylene. 24.The microtitration plate according to claim 23, wherein the receptacles(3) have a wall portion (10) of a very small wall thickness adjacent toa receptacle bottom (9) and have an upper wall portion (12) connected tothe plate (4).
 25. The microtitration plate according to claim 23,wherein the receptacles (3) have a collar of an increased wall thicknessas an upper wall portion (12) connected to the plate (4).
 26. Themicrotitration plate according to claim 23, wherein the receptacles (3)have a substantially cup-shaped bottom (9) and/or wall portions (10) ofa small wall thickness are substantially conical and/or a wall portion(11) adjoining it is of a wall thickness which gradually increasesupwardly.
 27. The microtitration plate according to claim 23, whereinthe receptacles (3) have molding points at the bottom (9) of thereceptacles.
 28. The microtitration plate according to claim 23, whereinthe frame (2) has a bordering (5) protruding from the underside (8)thereof at the edge of the plate (4).
 29. The microtitration plateaccording to claim 23, wherein the frame (2) has several edge-sidedmolding points.
 30. The microtitration plate according to claim 23,which is made of a plastic including a filler which does not containprotein.
 31. The microtitration plate according to claim 23, which ismade of a plastic filled with fiberglass.
 32. A microtitration plate foruse for automated polymerase chain reaction (PCR), comprising: a frame(2) which has a plate (4) wherein the plate (4) has a multiplicity ofholes (6′) molded of a polycarbonate a multiplicity of thin-wallreceptacles (3) having a wall thickness of from about 0.05 to about 0.25mm at least in one wall portion, and molded of a polycarbonate, with thereceptacles (3) fixedly connected to the plate (4) at the holes (6′) byfusing to each other both the polycarbonate of the plate (4) and thepolycarbonate of the receptacles (3) due to direct molding of thereceptacles (3) to the plate (4), the receptacles (3) having receivingportions (9, 10, 11) protruding from the underside (8) of the plate (4),and are accessible from the upper surface (7) of the plate (4) throughapertures (15), wherein the frame (2) and the receptacles (3) arecomposed of polycarbonates.